House prices in some of Britain’s wealthiest areas have had up to 25% wiped off their value in 12 months as Brexit turmoil continues, according to the estate agent Your Move. That has meant typical price falls in some cases of almost £500,000.

Meanwhile, data from the property website Rightmove revealed the average asking price of a London home had fallen below £600,000 for the first time since August 2015, and was well below its peak of almost £650,000 reached a few weeks before the Brexit vote in 2016.

The two sets of figures come days after Britain’s surveyors issued an especially gloomy assessment, fuelled by the lack of clarity over Britain’s departure from the EU. On Thursday, the Royal Institution of Chartered Surveyors (Rics) said house prices were falling at their fastest rate in six years, and that the outlook for sales was the weakest in two decades.

Your Move, which claims to be the UK’s biggest estate agent, said house prices in England and Wales rose 0.3% in December, but were falling in real terms when adjusted for inflation.

London is the area most obviously affected by the uncertainty, given the influence of wealthy foreign buyers, and Your Move said there had been big falls in a few key boroughs at the top of the market.

The average house price in Kensington and Chelsea, the UK’s most expensive place to buy a home, dropped by more than a fifth (21.2%), during the last 12 months, from £2.25m to £1.77m.

In Westminster, the second most expensive area, typical prices fell by a quarter (24.8%), from £1.93m to £1.45m.

Recent high-end sales in Westminster included a mansion on Belgrave Square bought for £60m. The five-storey stucco-fronted property had been on the market for almost a decade and was first listed at £100m.

Other London boroughs said to have experienced double-digit price falls over the past year include Hammersmith and Fulham, where the average property value dropped 19%, from £1.08m to £873,000, Camden (down 11.5%) and Tower Hamlets (down 11.3%).

Earlier this month, one property firm said sterling’s slump since the Brexit vote had turned the UK into a goldmine for foreign investors seeking a bargain.

However, prices in 10 London boroughs were up over the year.

According to Your Move, the annual rate of price growth for England and Wales is 0.6%, the lowest level since spring 2012.

Oliver Blake, the firm’s managing director, said that amid the political and economic uncertainty, “it is understandable why buyers and sellers may be taking a ‘wait and see’ approach to the property market”. However, he added that this meant homes may become more affordable to more people.

Rightmove said the UK market had undergone a muted and patchy start to 2019, with the lowest monthly price rise seen at this time of year since January 2012.

Its data showed the average asking price of a UK home had risen by 0.4%, or £1,207 in monetary terms, during the past month, taking it to £298,734.

Three out of 11 regions had price falls over the past month. These included London, where the average new seller asking price dipped 1.5% to £593,972.

In Wales, the monthly fall was 1.9%, while the East Midlands recorded a 0.3% decline.

The Rightmove website, which claims to feature about 90% of all properties for sale, said there had been a “patchy but active start to the year, with more northerly regions faring better in terms of pricing power and willingness to move than those farther south”.

It added that in London, a larger than usual seasonal fall had reduced average new seller asking prices to below £600,000 for the first time since August 2015. It said the capital had seen a slow start to 2019, with price falls, the uncertain political backdrop and the costs of moving apparently deterring some owners from coming to market.